This invention relates to poppet-type valves which are used in dispensing material such as sealant, adhesives, etc.
There is a growing need for valve assemblies usable in the fields of robotic and automatic application of materials such as sealants or adhesives. Prior art poppet-type valves, such as those sold by Loctite Corporation, Newington, Conn. and disclosed in Loctite's equipment catalog LT-859 8/84 entitled "Loctite/New Dimensions In Dispensing Systems Especially Designed For Loctite Adhesives and Sealants", having two positions, on and off, are known in the art. Such valves are generally motor driven to reach their two positions wherein they are either opened or closed. Prior art poppet-type valves are not known which are capable of movement between three or four positions. Furthermore, poppet-type valves of the prior art are not easily adjusted and readjusted with respect to the stroke of the piston acting on the valve stem.
When conventional poppet-type valves are utilized in robotic and automatic applications wherein the valve is attached to a robot arm and is moved by the robot in a predetermined pattern, problems arise due to the fact that the dispensing head velocity must change depending on the pattern being laid down. For example, if it is desired to lay a pattern of adhesive sealant, locking compound or other dispensed material in a desired pattern on a plate, the valve mounted on the arm of the robot would move along the desired dispensing path. It would normally move with its highest velocity along the straight line portion of said path. However, when the arm encounters a curved path, and particularly one of a small radius, the arm has to slow down to accumulate the necessary control information and make the mechanical movement because of the way the robots are controlled. At this point, a conventional two way valve which is in the opened positioned is unable to shut down to a slower dispense rate to account for the slower arm speed. Consequently, excess material is deposited at such locations which is undesirable.
It is a basic problem with respect to the control of such robots that they cannot move through an intrically shaped geometric pattern with curved and straight paths intermixed without changing speed. If the robot could move through such shapes without changing speed, the conventionally available poppet-type valve might be acceptable. However, since this is not the case, a valve assembly has been developed in accordance with this invention that will allow selectively different flow-rates which can be tied to the velocity of the robot.
The prior art poppet-type valve structures generally comprise a valve stem connected to a single cylinder piston rod. Since these valves have only two positions, open and closed, there is no easy way to adjust the stroke of such poppet-type valves to control precisely the dispensing rate. The way that this has been done in the past is to shave the material between the housing and the body of the valve and shorten the valve stem such as by cutting off a section of the stem and using a coupling to rejoin the stem sections for an overall shorter stem. In addition, the prior art valves can be motor driven or solonoid-activated to accomplish rapid opening and closing.
It is the purpose of this invention to provide an improved variable flow-rate dispensing valve assembly. The valve assembly is adapted for three or four position operation, and is particularly useful in conjunction with a robotic material application system.
The improved dispensing valve assembly of this invention is capable of providing a plurality of preselected material flow-rates. In accordance with one embodiment a three-way valve assembly is provided in including two preselected flow-rates of material and a shut-off position. In accordance with a more preferred embodiment of the present invention, a four-way valve assembly is provided including three preselectable material flow-rates of material and a shut-off position. The preselectable flow-rates may be easily obtained by an improved system for adjusting the stroke of the valve stem. The valve assembly of this invention finds particular application in a robotic system for applying the desired material to a workpiece.